Adhesives and/or coating materials--referred to hereinafter as adhesives--based upon aqueous alkali metal silicate solutions, that is, water glass solutions, have been known for a long time and are used on a large scale for many different purposes. Such adhesives are used, for example, for the preparation of coating materials, paints, and putties as well as for the gluing of wood, paper, ceramics, and mineral insulating materials.
Such adhesives are also used especially for the preparation of sheets or boards of mineral fiber laminated with metal foils that are preferred for use in the construction industry as insulating or sound-proofing materials.
Problems are frequently encountered when using and processing such adhesives, which problems may be caused, on the one hand, by a too early hardening or by an undesirable increase in the viscosity of the adhesive and, on the other hand, by the precipitation of fillers contained in the adhesive. Such effects considerably reduce the storage stability of the adhesives. An additional problem, particularly in connection with the last-mentioned application, is the water-resistance of the adhesives after they have been dried.
Adhesives or coating materials based upon water glass solutions that also contain clay minerals, such as kaolin, clay, or talc, as well as oxides or carbonates of the alkaline earth metals or of zinc, oxides or hydroxides of aluminum, and/or barium sulfate are known from the German Published Application (DE-AS) No. 24 60 543. Such compounds are suitable, for example, for the coating of mineral fiber substrates and must have characteristics of being only slightly brittle, having good compatibility with mineral fibers, as well as being water-resistant.
In contrast, German Published Application (DE-OS) No. 27 29 194 discloses that a content of oxides, hydroxides, and carbonates in such compounds considerably reduces the storage stability of the compounds since the content causes a strong increase in the viscosity as well as separations, which lead to the settling of the solids in a pasty mass that is very difficult to return to its original consistency, if at all. Thus, German Published Application (DE-OS) No. 27 29 194 describes adhesives and/or coating materials for mineral fibers based upon alkali metal silicate solutions that are characterized by a content of one or several materials with a mineralogical content of more than 20 percent of kaolinite as well as one or several water-soluble and alkali-resistant organic polymers. Such adhesives are said to have good storage stability, with regard to the settling of the solids, and a high water resistance of the bonds made with them.
The adhesives disclosed by each of the above-mentioned references represented an improvement of sorts to the state of the art at their respective times. However, as is demonstrated more fully below, both adhesives lack an adequate storage stability with respect to the settling out as well as the required water resistance of the obtained bond.